Method for operating blast furnaces



Patented July 19, 1949 METHGBJ'FDRE0PERATING}BLAST3 EUBNACES Henry T?Rudolf, Stenblenvilf; Ohio ApplicafionrJmuaryzeB, 19433; ,,SeriaLNo,a4-72-,204s

ITCIaifiL; (Cl. 75 -41) This invention. relatestto .improyementssinblashfurnaces-and. method. of .operating;the,=same.. The; iron blast furnace.is-

apparatus of: considerablee antiquity. It istusedqfonthepurposerofreducing. iron ore, which isrusua11y;- in -zth e form.:.otthe$oxr. idesE6203 0r Ee3Oi4 tO iron, by; causing the oxygen of the ore. to; combinewith carbonlmonoxide. (CO) formed by. the combustion of carbon-conetainingfueLlusualhncoke.

As. the demands, for" pig iron. haveincreasedj; the efiort' of thoseskilledlin the .artlhasflbeen. to devise blast furnacesof greaterproductive capacity Generally, speaking, thishas beentdoner byincreasing the size. of. the furnace: andefparticularly by enlarging thehearth area; As;a,-,v result of these efiorts, blast furnaces have been.built 'in'thisrco-untry havingzh'earths of T26ifet"in cliameter.and;1asv is well knowmzto build suc11" furnaces involvestremendous expense.so farvasi I" know, increasing the hearth area. isytlieonly' practicablemethod heretoforesuggested landjffil-E. lowed "for the purpose of"increasing the, produo; tion' of pig iron.-

I propose to increasethe production of "'Dig'iiron" in existingfurnaces. or" to providejnewfurnaces of greatly;increased-capacitywithoutlnrreasing the heartn'area': ln'connectiorrwithisuclrstruc turalchanges as I propose, I have developedanew method; of0peratin'gblast"furnaces-S0 asto increase greatly theirDIGdIlCtiCIF'Of*p1gfilO1Tif1"- a*un'it of time:

My invention involves the applicationmf anew thought to the operation ofblast furnaces whichi stated-broadly; is the-speeding up of' th'e rateofi fuel combustion without increasing the volumeof gas that passesupwardly througlr the volds in the burden; in the stack:

According to: my invention, more oxygen supplied for combustion: byincreasing 'theair blast volume; thereby generating: an increased thestack is accelerated .while-the volumerofEgas 50-- passing upwardlythrough: the stack zis'i'zlimiteda to-.;-substantia11y the; same ivolume-3S;.Wh6l1i?: the. furnaceis normally operating atvmaximum leaspacityi.

ASdS-rxWGllfkI-IOWII :tozthose skilled-drrz-the 11", a; 65 afiiilowsasla -but how to obtain; suclr-;a1qrat;ioyhas;i'

2"; blast furnace .is blown-on .v acwindgivolume" whichi is,.-.generally speaking, determined: experimen'etally. Such :factors ,aretakeniinto, consideration; as ,the character; of the fiiel'j and the"natlne of l thetburden with respectfto the sizejor, the partr alesandthe ovoid far-east Thewind volumeis 'fixe'd at that ,point," wherethe gas will pass free'IitHIf-f Wardly through; the. b'urdmwittfout suchresists ance aswilfcreate a b'ack pressure sufficient to:

impedethe'descentof the burden or causeittb hang in thestack,v Thereare, of course, other fa ctorswhicl'f are taken'in'to'consideration*in--determiningtlrewind volinnebut-sofarasmy-prociess'is'con'cernegi theyneednot be consideredmereiQ'mtrfewin'gl volume so; determined; the produce tionof pigiironinaunit"oftime'wlll-be*the-maxi:- nrum? f or a particular-furnace; alliother factors remainingiconstant.

Ifit be-attempted to 'increase the-wind volunre beyond the point soexperimentally determined? theoperation of th'e fiirnaee will beser-iouslyyimpaired. The gas volume will either notpass freely" througtfthe -burdn,-* th us creating a baek pressure which will impede itsdescent, or thefbiast will b'e so strong" as -to=--bl0w mucli of the-#-ore out 'of the furnacein the-form of dustj there-t by upsetting-thecarefully calculated= proportiorri of fuel to orey-causing th'e iurrraceto ibecome too hot 'as *wvel-l as 1 reducingthe"pig 'ironproduotihm Bymy improvement;- a given bla'st'ifurnace can? be operateds on a windvolnme in excess; by so muoh as may -be desired, o fathe volumeawhrchbeen: experimentally-1 determined i fori'maximum' plg'sirenproductionz.intithatifurnaceewithnut inn 3 terferingnmithithermovement:ofifitheeburdemandt withoutz'inereasingqthesdustilosss.Thislitzaccomplish by I wlthdrawingcthe sexcess rgas vOlum'e-mree ated'by theoincreasedoblastisosthatisubstantiallw theesamezvolumeeot gaspassesxthroughagthesburs' clenzas.whenrthelfurnacedsnormallyoperatingiat its maximunriproduotions.

v Fonmanrs/ears t a b l e d that-a las e u e nace; WQUldEODfiIfl B; mu fcie ly. when h CO/QQz IatiOsOf f the top; gas As -2 2-1): However;

45 this belief is no .lo l cl itenaloler Ratiosga'swlowtas;

lei zlilyhavevbeenr obtained; andritvis now believed on-,-goodauthority;that :the-ratio-mamloe ,rreducedq touasiilom; as; 1'21;Gen-erallyyspeaking argblasby furnaceels? mosttefiicient' thermally:andacls ermlecallyz when} thelwGQz 35in!) theetop; gas- 1s:v highestBut it:rr-lustloe :borne inmindethatc eigherhe.-; (3,02 content of thegasithe lower rw l-lbedtsicalos rific value. Pig iromrnay beg-produ ed fioally whezr the QQ/GOa ratiQs oft-the top; 8% is not heretofore beenknown. By my process such a ratio may be obtained, as well as any otherdesired ratio within practical limits, and this without affecting thecalorific value of the gas.

As is well known, the blast furnace gas is used to heat the air blastfor the furnace, to operate the blowing engines and, in an integratedplant, for many other purposes. Generally, the apparatus used has beendesigned to be operated on fuel of fairly definite heat value and it isimportant not to greatly reduce that value. By my process the productionof pig iron in a. unit of time may be greatly increased withoutsacrificing any of the heat value of the gas.

As heretofore stated, I propose to increase the wind volume toaccelerate fuel combustion and thereby produce an increased gas volume,but the increase in gas, or substantially all the increased gas volume,is withdrawn from the furnace so that approximately the same volume ofgas passes upwardly through the burden. The CO/COa ratio of the top gasin my process is thereby reduced and hence its calorific value isdecreased. However, I may mix with the top gas the withdrawn excess gasvolume, or any desired part of it, which has a high calorific value,thereby producing a gas mixture of substantially the same heat value asthat of the top gas which is produced in the normal operation of thefurnace.

But instead of mixing the two gas volumes as just described, I may useeach volume separately. The top gas may be used for low temperaturecombustion whereas the withdrawn gas may be used for higher temperaturecombustion. The choice will be made with reference to the nature of theapparatus at a particular plant and the desire of the operator inrespect to the heat value of the gas.

My invention may best be explained and more readily understood byreference to an ordinary blast furnace operated to produce the maximumquantity of pig iron in a given time. For example, a blast furnaceoperating on a Wind volume of 60,000 C. F. M. (cubic feet per minute) ofair at normal temperature and pressure will produce a top gas volume ofabout 84,000 C. F. M. at normal temperature and pressure and willproduce a certain number of tons of pig iron in a unit of time. This topgas contains, roughly, about 40% carbon gases and about 60% nitrogen.There will also be a small percentage of hydrogen due to moisture in theair and the burden, but this may be disregarded for my purposes.

The carbon gases in the top gas comprise, on the average, about 26.6% Cand about 13.3% CO2, so that the CO/COa ratio is about 2:1. The volumes,in my example, are substantially 22,400 C. F. M. of CO and 11,200 C. F.M. of C02. The bosh gas contains roughly about 40% CO, or a volume of33,600 C. F. M. Hence, it is plain that only about one-third of theavailable CO is used in the reduction process and becomes CO2 by unionwith the oxygen of the ore.

The 11,200 C. F. M. of C0 thus used will reduce a certain quantity ofore in a given time. If we can lower the CO/COz ratio to 1:1, thusutilizing an additional 5600 C. F. M. of C0. or a total of 1.5 times asmuch CO, we should be able to reduce an additional percentage of ore inthe same time by the same proportion, provided we can make the burdentravel 1.5 times as fast.

The rate of the down travel of the burden can be increased by removingthe bulk of the coke more rapidly, so that the ore can settle faster,whereby more oxygen of the ore is available for union with the CO toproduce CO2 in increased quantity. In the example given, I propose tospeed up the rate of coke combustion 1.5 times. It is known thatcombustion proceeds roughly as the rate of application of the oxygen ofthe air to the carbon of the coke. Generally speaking, it takes about'75 cubic feet of air at 62 F. and 30 inches of mercury to burn onepound of carbon. But this air volume is subject to variation on accountof changes in the temperature and humidity of the air and in barometricpressure. The air volume will also vary in accordance with the carboncontent of the fuel. In my process it is desired to increase the rate ofdown travel of the burden 1.5 times and this can be accomplished byspeeding up the combustion of the fuel to 1.5 times the normal rate.This means that 1.5 times as much oxygen will be supplied in the sametime period which, in turn, means that the wind volume must be increased.5 times. Thus, in my example of a furnace operating on a blast of60,000 C. F. M., the blast must be increased to 90,000 C. F. M. in orderto increase the combustion rate 1.5 times. Thus, the bulk of the coke ismore rapidly removed and it follows that the burden will descend morerapidly in the stack, providing that it is not prevented from so doingby the increase in gas volume which is produced by the increased airblast.

Such an increase in blast volume would be unthinkable if it were not forthe improvements I propose in the construction and operation of thefurnace. If, in my example furnace, in which, when operating atcapacity, 84,000 C. F. M. of gas passes upwardly through the burden, thegas volume is increased to 126,000 C. F. M., it will readily beunderstood that the back pressure created will be so great as to causethe burden to hang in the stack. However, I provide means for removingthis increased part of the gas volume from the furnace before it canenter the stack, thus maintaining the volume of gas that passes upwardlysubstantially constant. This I accomplish by the means and method now tobe described.

To make my explanation clear, I have appended hereto a drawing showing ablast furnace with my improvements applied. This drawing is onlyillustrative and is entirely diagrammatic, no attempt being made to showany particular proportion of parts or precise location of elements.

I The single figure of the drawing is a vertical section of a blastfurnace comprising th conventional elements, hearth I, bosh 2 and stack3. At the top I show only the large bell 4. From the top, the gas passesthrough the downcomer 5 into any form of cleaning apparatus 6. The usualbustle pipe is marked 1 and from this the air blast passes through thetuyeres 8, which are of the usual or desired number and of typicalconstruction. Thus far, the parts of the furnace described may be of anywell known construction, size and shape.

My improvement, structurally, resides in the provision of gas escapeopenings or exhaust ports 9, of which a plurality are provided, andwhich are located at or about the bosh line. The exhaust ports 9 allcommunicate with a collector pipe or manifold 10 which may surround thefurnace in the same manner as the bustle pipe 1. An exhaust pipe H leadsfrom the collector 5 nine-.- lkto hecleanine apparatusgfiz hisg a terfeaturev will; bee incornorated 5 wh never; t. s 1. sit s; to. mix; the;withdrawn.- e ess. volume easswiththei qp easemanatins r m he fu nacnthe; usual. manner.- H wever, where i s desiredto use; theses.volumesseparate y. the xmust-p pe. ILmav. 1ead-: o-anv.- th r form ofcleanin and: p cessing apparatus. so that; the. excesseas of. high,calorific. value may e usedseparatelv. from the ord nary. pas.

At anyv convenientzplase in thapipe Izplaeea valve V which may be eitherautomatically or. manually-controlled so as, to.regulate. the escapefegas. .from..the h hthrough heports 9; The mechanism. for. operatingthe. valve, may be any of; theknown ratio control devices, or the valve.maybe: of; the. pressure; responsive. type. which. will-open. only.whenethegas. pressure in the.. bosh. reachesa predeterminedspoint.Thus, thevalve. V is. used for the purposeof. controlling andvregulating the-quantity of gas in. the bosh which will; be. permitted,to escape. andthus preventing it fromipassingupwardly.throughthestach Bythis arrangement. the. volume of gaspassing upwardly. through the.burden. may. be. maintained substantially the same as the gas. volumethat Passes throughthestackin the normal operation-of the. furnace. Intheexample heretofore giyen of afurnace. normally operating on a windof. 60,000 C. F; M. andthe blast is increased to 90Q00- C. F. M., the.gas volume is increased from: about; 84,000 C. F.- M. to 126,000 C. F.M. This increaseof approximately llOOtl C. F. M. in, the .gas. volumemay substantially.v all be with drawn through the. exhaust ports 9; andthis result-will be accomplishedsby a proper regulationof the valve V.

It will,. of course, be understoodthat once. a blast. furnaceis equippedwith. my improvements it- .nee.d notbecontinuously operated inaccordance with my process. That is to say, it'may be desirable at timesto. operate the furnace in h normal man r so. asto rodu ly htollrthseof: pig iron corresponding toits rated capacity. Atsuchtimes.the,- valve V may be permanently closed.- and thus nonev ofthe gasvolume withdrawn prior to its. entry intothe. 1 39 5,. In such cases, ofcourse, the-wind-volmneis ;reduced=toits normakfieure.

I have shown and describedtheexhaustports or outlets. 9;;aslocated. ator about the bosh line. This is the preferred location oi said portsbecause at this point-the.gaspressureis lowest per unit cross sectionalarea of the. furnace. Moreover, at this point dust and finepa'rticleshave completed melting or have aggljcjin erated so that there is little''o r no danger thatthe increase in gas pressure will cause; anyincrease. at all;

theidust loss.

Eroin the foregoing description of the construction of ablast furnaceembodying my improvements and of operation thereof, I believe that myinvention will be clear to those skilled ln,the.art. Ob.V10.I1ly,- mystructural; improve-.. ments and new method may be appliedt and used-inconnection with, existing. furnaces. It islikewise clear that new.furnaces maybe built embodying my improvements from the start and thatsuch. furnaces.. maybe madeverymuch smallerand-yet have. the samecapacity as the large furnagesmow in use.- Thus, there results. aconsiderable saving in building and maintenance expense.

Because of the fact that in my furnace operated in accordance with mymethod the rate of respondingly reate burde o umes. He e,

more. o h GQ the I gas wi n te-i with; he oxygen or: the or n sulinam-ereaten reduction in;th eiventime-per od:. ne mi thtasah ehepercentagecf-zthaCol s thusmn erte nt 0G2, t follows t at; the 01/. Qaati f? he:- top gas ismormsnonfinelr: reduc whi h. ofy ourse s.ccompanie by. a. eduelenl nthe heat: va ue- 0.1; that gas; E r exampliwhenethe fur ac s, op ating normally and he; CQZQQa atio. is on heavera eapsroximate v he. alor fi value (iii-the. easis subst nti l y- 87B t:,-u-; p r. cubiceot. When; the. ratio. is edu ed to: 11 he lerific.value. of theas; falls o approx mate y: 65:41:13.1 t; 11.- p rcubidioot. may-be a.seri-. ils-loss. i:heat-..va1ue.in. v.ve.niplant;.Wh r the toves. for. he. irv wa ta dthe ow ng; n nes. andaxiliary equipment. aredesien d to, ope ate; on. ga havin a. high r,heating value...

However. bymy process. thereneedrbe. no ,re.-.,. sulting, loss inheating; value 0.f.3th e stars. Thisis because. the .ewithdrawne.X6.8.5.8. gas. volume; taken from the bosh-may be .mixe.dj=,with; the.top gas, as. heretofore described. Thegas volumethus with drawnvcontains nearly..40%.CO and; therefore, has a calorific; value. of;approximately 130.05; B. t. u. per cubic foot-.- Thus,. in theexample.furnace. operation heretofore described; the; normal. gasvolume;..is..8.4 000.0; M'.: Under my. process whereby. the CO/COz.ratio .has: been reduced to 1:1, the heating.' value-30f that volumeofz-gasis; 65.4.3. ti u. pert cubicv foot. The in-. creased'gas volumeof"42;000 611M. withdrawn from. the bush has aheating. value of 130.05-B; t. u. per cubic vfoot. lfswemix thesetwo volumes weshallthenget atotal of 126;!)00 C. F. M. of gas having a calorificvalue ofapproximately 875. t. u. pei cubic foot, Wh'iChdS-the same heating valueof the top -gastheiurnace hetd: when it was operating" normally. andwhen the CO/CO2- ratiois 2:1. 7

Thus in accordance with-the-foregoing, it will be seen that by myprocess'the production of pig iron in a given unit of time may be verygreatly re s w thout any. orres en ms l e e i n e hee n va ii eii e as'wi be understcod; however, that I; do not contemplate that alwaysand ineyery casev the entire. excess volume of gas withdrawn from the bosh.shall-be migedwith the topgas. There may be. cases where the reductionin, .he ating value of the. top gas is onor sufiicient consequence torequire. the ,mixing ,.ot the. two 2 gas volumes and Where the. separateuse of the- .bos'h.igas may.-be. initselfof considerable value In. he.xam le s fl i' l I; .3."? m e less arbitrarily elected totreduce; the.-(IO/CO2 ratio from 2-::1.to 151.; This -,of; course, is not always.necessary nor may it be desirable. always 3 to make such agreat'reductionanq the ratio and; such a correspondingly great increase-in--,the. air blast volume. Wha .I, propqseto-do in any casev is todetermine. the :QQKGOz; ratio ,of, the top gas when the, ;furna ce;is.-operating atrits rated maxi mum-capacity. and thento;..red.uce,.that ratio to any desirable pointlimitlngmyseltperhaps tothe ratio of li; 1. .whichgismow onigood :authority .believed to beattainable in an economic ore reduction process. However, it will beseen that if we start off with a normal ratio of 2:1, it may be desiredto reduce this only to, say, 1.5:1. In such a case, instead of usingonly 33 of the available CO in the reduction process, we shall useapproximately 40% of the CO. This means an increase of 20% and, hence,in that case the air blast volume would be increased by 20%.

An important result of the use of my improved blast furnace and methodof operation is that the temperature gradient of the furnace will bevery much steeper. In the ordinary blast furnace in normal operation,the temperature gradient is estimated to be from about 3300 F. to about400 F. whereas in my process the gradient will be from a higher point,say, 3600 F. down to 100 F. This means that more of the heat of the gasvolume is given up in the exchange in the reduction process with theresult that the various sections of the burden will reach the differentzones of the furnace at more nearly the proper temperature. It is alsopossible that because in my process the gas emerges at the top at a somuch lower temperature and pressure, more gas may pass upwardly throughthe stack than in the normal operation of the furnace.

I am aware of the fact that it has heretofore been proposed to speed upthe rate of coke combustion in a blast furnace by oxygen enrichment ofthe blast, that is to say, by adding pure oxygen to the air blast.Doubtlessly, this will have the effect of speeding up combustion which,as heretofore stated, proceeds roughly as the rate of application ofoxygen to the carbon in the fuel. However, such oxygen enrichment of theblast is not practicable, for the reason that there results a seriousunbalance of the components of the gas generated. It will be quiteapparent that the percentage of nitrogen in the gas generated by such anoxygen enriched air blast will be very much reduced and this willseriously impair the operation of the furnace. It is well known that thefunction of nitrogen in the gas is that of a heat-transferring agentand, obviously, where the nitrogen content is seriously reduced, theheat exchange in the furnace is impaired and the ratio of direct andindirect reduction will be altered so as to cause a much higherpercentage of direct reduction. This, of course, will radically andadversely affect the efficiency of the furnace.

I am also aware of the fact that blast furnaces have at times beenoperated on what is called slack wind. That is to say, whenever it hasbeen desired to operate a furnace at less than its maximum capacity, thewind volume has been reduced. After such reduction, and when it wasdesired to restore the operation to normal maximum capacity, the windvolume has been increased. My process is, of course, readilydistinguished from this slack wind operation because I increase the airblast volume above that which is normally used when the furnace isoperating at its maximum capacity.

Whenever throughout this specification, and in the appended claims, Iuse the expression increasing the production of pig'iron or increasingthe capacity of the furnace, it is to be understood that I mean anincrease over and above the rated maximum capacity of the furance. Forexample, if the capacity of a blast furnace to produce its maximumtonnage of pig iron is defined as that condition under which the furnaceburns 60 pounds of coke per 24 hours per cubic foot of volume of thefurnace measured from the center line of the tuyeres to the stock line,then it is that capacity which I increase. In the example given, afurnace operated in accordance with my process would burn pounds of cokeper 24 hours per cubic foot of volume of the furnace measured as abovestated. By my process a blast furnace which, when operating at itscapacity, produces approximately 1000 tons of pig iron per 24 hours maybe operated so as to have a capacity of approximately 1500 tons per 24hours.

It will be understood that the figures given throughout thisspecification for ratios, volumes and percentages are not intended to beexactl but are fair approximations of average figures. Nor are thesefigures constant because, as is well known to the blast furnaceengineer, they vary from furnace to furnace and even in the same furnacefrom time to time. There are, of course, many other factors that affectthe operation of a blast furnace and its production of pig iron butthese I have not thought it necessary to mention herein because theywill affect a blast furnace operated by my process in the same way andproportionately.

On more recently built blast furnaces, there usually is a good deal morewind volume available than is normally used and in such cases sufllcientexcess capacity may be found so that the blowers can be used in myprocess Without change. On older furnaces it may be necessary toincorporate new blowers having sufiicient capacity for my purposes. Sofar as the tuyeres are concernecl, it will probably be necessary toincrease their cross-sectional area to meet the higher wind volume whilemaintaining the pressure substantially constant. These things canreadily be taken care of by the skilled blast furnace operator whodesires to use the new process herein described.

I claim as my invention:

The method of operating a blast furnace to increase the production ofpig iron which comprises increasing the air blast volume to speed up therate of fuel combustion and thereby increase the rate of down travel ofthe burden, and controlling the gas volume entering the burden tomaintain the rate of up travel of the gas substantially constant.

HENRY T. RUDOLF.

REFERENCES CITED The following referenices are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 117,246 Bessemer July 25, 18711,357,781 Koppers Nov. 2, 1920 OTHER REFERENCES Blast Furnace Practice,1st ed, page 161, by Sweetser; published in 1938 by McGraw-Hill BookCo., New York.

Blast Furnace Practice, vol. 2, page 260; by Clements; published in 1929by Ernest Benn Limited, London.

Transactions of the American Mining and Metallurgical Engineers, vol.120, page 72; published by the A. I. M. E., New York.

